The present invention relates to perpendicular magnetic recording media with improved signal-to-medium noise ratio (xe2x80x9cSMNRxe2x80x9d) and thermal stability, which media include a pair of vertically spaced-apart perpendicular ferromagnetic layers which are anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d) across a non-magnetic spacer layer, and a method of manufacturing same. The invention is of particular utility in the fabrication of data/information storage and retrieval media, e.g., hard disks, having ultra-high areal recording/storage densities.
Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called xe2x80x9cperpendicularxe2x80x9d recording media have been found to be superior to the more conventional xe2x80x9clongitudinalxe2x80x9d media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a xe2x80x9csingle-polexe2x80x9d magnetic transducer or xe2x80x9cheadxe2x80x9d with such perpendicular magnetic media.
It is well-known that efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (i.e., as compared to the magnetic recording layer), magnetically xe2x80x9csoftxe2x80x9d underlayer, i.e., a magnetic layer having a relatively low coercivity of about 1 kOe or below, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the xe2x80x9chardxe2x80x9d magnetic recording layer having relatively high coercivity of several kOe, typically about 3xe2x80x946 kOe, e.g., of a cobalt-based alloy (e.g., a Coxe2x80x94Cr alloy) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer. In addition, the magnetically soft underlayer reduces susceptibility of the medium to thermally-activated magnetization reversal by reducing the demagnetizing fields which lower the energy barrier that maintains the current state of magnetization.
A typical perpendicular recording system 10 utilizing a vertically oriented magnetic medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 3, 4, and 5, respectively, indicate the substrate, soft magnetic underlayer, at least one non-magnetic interlayer, and vertically oriented, hard magnetic recording layer of perpendicular magnetic medium 1, and reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of single-pole magnetic transducer head 6. Relatively thin interlayer 4 (also referred to as an xe2x80x9cintermediatexe2x80x9d layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 3 and the hard recording layer 5 and (2) promote desired microstructural and magnetic properties of the hard recording layer. As shown by the arrows in the figure indicating the path of the magnetic flux xcfx86, flux xcfx86 is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through vertically oriented, hard magnetic recording layer 5 in the region above single pole 7, entering and travelling along soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through vertically oriented, hard magnetic recording layer 5 in the region above auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of each polycrystalline (i.e., granular) layer of the layer stack constituting medium 1. As apparent from the figure, the width of the grains (as measured in a horizontal direction) of each of the polycrystalline layers constituting the layer stack of the medium is substantially the same, i.e., each overlying layer replicates the grain width of the underlying layer. Not shown in the figure, for illustrative simplicity, are a protective overcoat layer, such as of a diamond-like carbon (DLC) formed over hard magnetic layer 5, and a lubricant topcoat layer, such as of a perfluoropolyethylene material, formed over the protective overcoat layer. Substrate 2 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Alxe2x80x94Mg having an Nixe2x80x94P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; underlayer 3 is typically comprised of an about 500 to about 4,000 xc3x85 thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeCoC, etc.; interlayer 4 typically comprises an up to about 300 xc3x85 thick layer of a non-magnetic material, such as TiCr; and hard magnetic layer 5 is typically comprised of an about 100 to about 250 xc3x85 thick layer of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, B, and Pd, iron oxides, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 xc3x85 thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, Pt, W, and Fe, and each of the alternating thin, non-magnetic layers of Pd or Pt is about 1 xc3x85 thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
In general, an improvement in the signal-to-medium noise ratio (SMNR) of perpendicular magnetic recording media such as described above can be obtained by decreasing the average volume V of the magnetic grains and/or by decreasing interactions between the grains. However, in either instance, thermal stability of the perpendicular media is compromised.
In view of the above, there exists a clear need for improved, high areal recording density, perpendicular magnetic information/data recording, storage, and retrieval media which exhibit both increased signal-to-media noise ratios (SMNR) and thermal stability. In addition, there exists a need for an improved method for manufacturing high areal recording density, perpendicular magnetic recording media which exhibit both increased SMNR and thermal stability, which media can be readily and economically fabricated by means of conventional manufacturing techniques and instrumentalities.
The present invention addresses and solves problems attendant upon the design and manufacture of high bit density perpendicular magnetic media, e.g., obtainment of high SMNR without compromising the thermal stability of the media, while maintaining all structural and mechanical aspects of high bit density recording technology. Moreover, the magnetic media of the present invention advantageously can be fabricated by means of conventional manufacturing techniques, e.g., sputtering.
An advantage of the present invention is an improved, high areal recording density, perpendicular magnetic recording medium.
Another advantage of the present invention is an improved, high areal recording density, anti-ferromagnetically coupled (AFC), perpendicular magnetic recording medium having increased signal-to-noise ratio (SMNR) and thermal stability.
Still another advantage of the present invention is a method of manufacturing an improved, high areal recording density, perpendicular magnetic recording medium.
Yet another advantage of the present invention is a method of manufacturing an improved, high areal recording density, anti-ferromagnetically coupled (AFC), perpendicular magnetic recording medium having an increased signal-to-noise ratio (SMNR) and thermal stability.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to one aspect of the present invention, the foregoing and other advantages are obtained in part by a high areal recording density, anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d) perpendicular magnetic recording medium, comprising:
(a) a non-magnetic substrate having a surface; and
(b) a layer stack formed over the substrate surface, the layer stack comprising, in overlying sequence from the substrate surface:
(b1) an underlayer comprised of a magnetically soft ferromagnetic material or a plurality of layers of magnetically soft ferromagnetic material separated by thin, non-magnetic spacer layers;
(b2) at least one non-magnetic interlayer;
(b3) a perpendicularly anisotropic stabilization layer comprised of a hard ferromagnetic material;
(b4) a non-magnetic spacer layer; and
(b5) a perpendicularly anisotropic main recording layer
comprised of a hard ferromagnetic material;
wherein the perpendicularly anisotropic stabilization layer (b3) and the perpendicularly anisotropic main recording layer (b5) are anti-ferromagnetically coupled (AFC) across the non-magnetic spacer layer (b4) to orient the magnetic moments thereof anti-parallel and thereby provide the medium with increased SMNR and thermal stability.
According to embodiments of the present invention, the non-magnetic spacer layer (b4) is from about 2 to about 15 xc3x85 thick, e.g., from about 4 to about 11 xc3x85 thick and selected to maximize anti-ferromagnetic coupling between stabilization layer (b3) and main recording layer (b5), comprising a material selected from the group consisting of Ru, Rh, Ir, Cr, Cu, Re, V, and their alloys; and the layer stack (b) optionally further comprises:
(b6) at least one ferromagnetic interface layer at at least one interface between the non-magnetic spacer layer (b4) and the main recording layer (b5) and/or the stabilization layer (b3), wherein:
the at least one ferromagnetic interface layer (b6) is present at the interface between the non-magnetic spacer layer (b4) and the main recording layer (b5), or the at least one ferromagnetic interface layer (b6) is present at the interface between the non-magnetic spacer layer (b4) and the stabilization layer (b3), or the at least one ferromagnetic interface layer (b6) is present at the interfaces between the non-magnetic spacer layer (b4) and each of the main recording layer (b5) and stabilization layer (b3).
In accordance with embodiments of the present invention, the at least one ferromagnetic interface layer (b6) comprises an about 1 monolayer to an about 40 xc3x85 thick layer of a ferromagnetic material having a saturation magnetization value Ms greater than 300 emu/cc, and according to particular embodiments of the present invention, the at least one ferromagnetic interface layer (b6) comprises a layer of a high moment element or alloy selected from Fe, Co, FeCo, and their alloys containing at least one element selected from Cr, Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Ni, Cu, Ag, Au, and W, wherein the concentration of Co, Fe, or CoFe in the alloy is constant or varies across the thickness of the at least one interface layer (b6) from higher near an interface with the non-magnetic spacer layer (b4) to lower near an interface with the stabilization layer (b3) or the main recording layer (b5).
According to certain embodiments of the present invention, the layer stack (b) further includes at least one additional stacked pair of layers between the main recording layer (b5) and the non-magnetic spacer layer (b4), consisting of a magnetic layer with perpendicular magnetic anisotropy and a non-magnetic spacer layer, such that layer stack (b) comprises alternating magnetic layers and non-magnetic spacer layers, and the magnetic energies of the magnetic layers and coupling energies between magnetic layers are selected to provide anti-parallel alignment of magnetic moments of adjacent magnetic layers during data storage in the medium.
In accordance with particular embodiments of the present invention, the stabilization layer (b3) and main recording layer (b5) each comprise an about 3 to about 300 xc3x85 thick layer of a ferromagnetic alloy selected from CoCr and CoCr containing at least one element selected from Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Fe, Ni, and W, or the stabilization layer (b3) and the main recording layer (b5) each comprise an about 10 to about 300 xc3x85 thick layer of a (CoX/Pd or Pt)n, (FeX/Pd or Pt)n, or (FeCoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 1 to about 25, each of the alternating layers of Co-based, Fe-based, or CoFe-based magnetic alloy is from about 1.5 to about 10 xc3x85 thick, X is one or more elements selected from the group consisting of Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Ni, Cr, and W, and each of the alternating layers of non-magnetic Pd or Pt is from about 3 to about 15 xc3x85 thick.
According to embodiments of the present invention, the non-magnetic substrate (a) comprises a material selected from the group consisting of: Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other non-magnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof;
underlayer (b1) comprises an about 500 to about 4,000 xc3x85 thick layer comprised of at least one soft ferromagnetic material selected from Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoTaZr, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeTaC, FeAlN, FeTaN, CoFeZr, FeCoB, and FeCoC; and
the at least one interlayer (b2) comprises an about 10 to about 300 xc3x85 thick layer or layers of at least one non-magnetic material selected from Pt, Pd, Ir, Re, Ru, Hf, and alloys thereof, or a hexagonal Co-based non-magnetic alloy with at least one of Cr, Pt, Ta, and B; and the medium further comprises:
(c) a protective overcoat layer on the main recording layer (b5); and
(d) a lubricant topcoat layer over the protective overcoat layer (c).
Another aspect of the present invention is a method of manufacturing a high areal recording density, anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d) perpendicular magnetic recording medium, comprising the steps of:
(a) providing a non-magnetic substrate having a surface; and
(b) forming a layer stack over the substrate surface, comprising the following sequential steps for forming an overlying sequence of layers from the substrate surface:
(b1) forming an underlayer comprised of a magnetically soft ferromagnetic material or a plurality of layers of magnetically soft material separated by thin, non-magnetic spacer layers;
(b2) forming at least one non-magnetic interlayer;
(b3) forming a perpendicularly anisotropic stabilization layer comprised of a hard ferromagnetic material;
(b4) forming a non-magnetic spacer layer; and
(b5) forming a perpendicularly anisotropic main recording layer
comprised of a hard ferromagnetic material;
wherein the perpendicularly anisotropic stabilization layer and the perpendicularly anisotropic main recording layer are anti-ferromagnetically coupled (AFC) across the non-magnetic spacer layer to orient the magnetic moments thereof anti-parallel and thereby provide the medium with increased SMNR and thermal stability.
According to embodiments of the present invention, step (b4) comprises forming an about 2 to about 15 xc3x85 thick layer, e.g., from about 4 to about 11 xc3x85 thick, of a non-magnetic material selected to maximize anti-ferromagnetic coupling between stabilization layer (b3) and main recording layer (b5), comprising a material selected from the group consisting of Ru, Rh, Ir, Cr, Cu, Re, V, and their alloys; and the method optionally further comprises the step of:
(b6) forming at least one ferromagnetic interface layer at at least one interface between the non-magnetic spacer layer and the main recording layer and/or the stabilization layer, wherein step (b6) comprises one of the following alternatives:
(i) forming the at least one ferromagnetic interface layer at the interface between the non-magnetic spacer layer and the main recording layer;
(ii) forming the at least one ferromagnetic interface layer at the interface between the non-magnetic spacer layer and the stabilization layer; and
(iii) forming the at least one ferromagnetic interface layer at the interfaces between the non-magnetic spacer layer and each of the main recording layer and stabilization layer.
In accordance with particular embodiments of the present invention, step (b6) comprises forming an about 1 monolayer to an about 40 xc3x85 thick layer of a ferromagnetic material having a saturation magnetization value Ms greater than 300 emu/cc, comprising a high moment element or alloy selected from Fe, Co, FeCo, and their alloys containing at least one element selected from Cr, Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Ni, Cu, Ag, Au, and W, wherein the concentration of Co, Fe, or CoFe in the alloy is constant or varies across the thickness of the at least one interface layer from higher near an interface with the non-magnetic spacer layer to lower near an interface with the stabilization layer or the main recording layer.
According to additional embodiments of the present invention, step (b) further comprises the sequential steps of:
(b6) forming a non-magnetic spacer layer in overlying contact with the main recording layer formed in step (b5); and
(b7) forming a perpendicularly anisotropic main recording layer in overlying contact with the non-magnetic spacer layer formed in step (b6);
wherein the above sequence of performing step (b6) followed by step (b7) is performed one or more times and step (b) comprises a still further step (b8) of forming at least one ferromagnetic interface layer at at least one interface between the non-magnetic spacer layers and the main recording layers and stabilization layer.
In accordance with particular embodiments of the present invention, steps (b3) and (b5) for forming the stabilization and main recording layers each comprise forming a perpendicularly anisotropic, hard ferromagnetic layer selected from the following alternatives:
(i) an about 3 to about 300 xc3x85 thick layer of a ferromagnetic alloy selected from CoCr and CoCr containing at least one element selected from Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Fe, Ni, and W; and
(ii) an about 10 to about 300 xc3x85 thick layer of a (CoX/Pd or Pt)n, (FeX/Pd or Pt)n, or (FeCoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 1 to about 25, each of the alternating layers of Co-based, Fe-based, or CoFe-based magnetic alloy is from about 1.5 to about 10 xc3x85 thick, X is one or more elements selected from the group consisting of Pt, Ta, B, Mo, Ru, Si, Ge, Nb, Ni, Cr, and W, and each of the alternating layers of non-magnetic Pd or Pt is from about 3 to about 15 xc3x85 thick.
According to embodiments of the present invention, step (a) comprises providing a non-magnetic substrate comprising a material selected from the group consisting of: Al, NiP-plated Al, Alxe2x80x94Mg alloys, other Al-based alloys, other nonmagnetic metals, other non-magnetic alloys, glass, ceramics, polymers, glass-ceramics, and composites and/or laminates thereof;
step (b1) comprises forming an underlayer comprising an about 500 to about 4,000 xc3x85 thick layer comprised of at least one soft ferromagnetic material selected from Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoTaZr, CoFe, Fe, FeN, FeSiAl, FeSiAlN, FeTaC, FeAlN, FeTaN, CoFeZr, FeCoB, and FeCoC;
step (b2) comprises forming at least one interlayer comprising an about 10 to about 300 xc3x85 thick layer or layers of at least one non-magnetic material selected from Pt, Pd, Ir, Re, Ru, Hf, and alloys thereof, or a hexagonal Co-based nonmagnetic alloy with at least one of Cr, Pt, Ta, and B; and the method comprises the further steps of:
(c) forming a protective overcoat layer on the main recording layer; and
(d) forming a lubricant topcoat layer over the protective overcoat layer.
Still another aspect of the present invention is a high areal recording density, anti-ferromagnetically coupled (xe2x80x9cAFCxe2x80x9d) perpendicular magnetic recording medium, comprising:
(a) a pair of vertically spaced-apart, perpendicularly magnetically anisotropic layers each comprised of a hard ferromagnetic material; and
(b) means for anti-ferromagnetically coupling the pair of vertically spaced-apart layers to orient the magnetic moments thereof anti-parallel and thereby provide the medium with increased SMNR and thermal stability.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not limitative.